The Boeing 747-100 jetliner that crashed off Long Island was operated by TWA for all but one of its nearly 25 years in service. For exactly 365 days in the mid-1970s, the plane belonged to the Imperial Iranian Air Force.
No connection has been established between that fact and the fiery midair explosion that knocked the plane out of the sky last week, killing all 230 on board.
But it was during the jet's 12-month stint in the Iranian military that another TWA 747 owned by Iran was destroyed near Madrid in a midair explosion much like the one that destroyed Flight 800 off Long Island last week. It was the only other time a 747 has burst into flames in midair.
No cause was determined in the Madrid crash, but officials believe that either an unusual blast of wind tore the left wing off or a stray electrical spark from a fuel-system pump, perhaps triggered by lightning, ignited jet fuel fumes inside the left wing.
As a result, the Federal Aviation Administration in 1976 ordered 747 wings checked for fuel leaks, and Boeing subsequently took steps to make the fuel system safer.
But it's not known whether those safeguards were taken on the 747 that burst into flames off Long Island. At the time, the plane was exempt from civil-aviation rules and directives because it was in military service.
Boeing spokesman Doug Webb said he could not say whether the fuel-system upgrades were made once the jet was repurchased by TWA in December 1976.
The jet had been continuously operated by TWA since then, according to a records review conducted for The Times by Kolbenschlag Aviation Services of Falls City, Ore.
TWA spokesman Don Morrison said he could not say specifically why the Long Island jet was sold to Iran and repurchased but said the transaction occurred during a time when airlines were adjusting the size of their fleets in reaction to market conditions.
Yesterday, investigators announced the results of preliminary analysis of Long Island 747's cockpit and flight data recorders. The voice recorder showed no signs of a crisis among the cockpit crew, and some analysts are citing that as evidence that the crash was not caused by a mechanical failure. However, the NTSB report on the Madrid explosion noted that the voice recorder also provided few clues in that crash.
NTSB Vice Chairman Robert Francis did say yesterday that one of the TWA pilots noted an "erratic fuel-flow gauge" two minutes before the recording ends but didn't mention the problem again.
The record of the Madrid investigation provides authorities with an extensive analysis of how a catastrophic mechanical failure can detonate a 747 jumbo jet. NTSB records obtained by The Seattle Times describe a 30-month investigation by a team of U.S. experts.
Boeing had bought the Madrid jet from TWA, converted it to a freighter and sold it to the Iranian air force in March 1976. A few months later, four Boeing trainers were on board with 13 Iranian military personnel as the aircraft left Teheran on a military logistics flight. It was descending into Madrid for a refueling stop in a thunderstorm when witnesses reported an in-flight explosion and fire at about 6,000 feet.
The explosion scattered debris over a wide area, with the jet's fuselage, right wing, four engines, tail and inboard stub of the left wing forming the main wreckage site. Parts of the left wing, including the wing tip, landed in the same area, five miles from the main site, with the rest of the left wing landing about a mile from the fuselage.
So far, authorities trying to solve the Long Island crash haven't released specific information about where major groups of wreckage lie 120 feet beneath the surface of the Atlantic. As of yesterday only two of the jet's four engines had been located by sonar equipment and dive teams.
In the Madrid crash, the focus quickly turned to the left wing, which was taken to a Federal Aviation Administration lab in the United States for analysis.
Most of the NTSB's report, as well as supporting documents obtained by The Times, speaks to the possibility of a stray electrical spark, perhaps from a pump that moves fuel between tanks, detonating the left wing.
Forensic experts from the FBI and Boeing analyzed eight samples of residue from the left-wing fuel tanks and a sealed empty compartment, called the dry bay, near the left outboard engine. They found no evidence of explosives or residue of explosives.
Yet the fiberglass lead edge above the engine was severely burned by fire blasting forward into the slip stream. Metallurgists established that the upper left-wing skin tore off, releasing some 54,000 gallons of jet fuel, after the fiery blast was touched off near the left outboard engine.
In June 1976, before those findings were complete, the FAA issued an airworthiness directive, ordering 747 operators to inspect for fuel leaks in the dry bay. Most found leaks.
As investigators continued to puzzle over the Long Island crash yesterday, declining to zero in on a bomb, missile or mechanical failure as the cause of the TWA crash, FAA Administrator David Hinson met in Seattle with Boeing chairman Phil Condit.
The visit was unscheduled and concerned "routine business matters between the FAA and Boeing," said company spokesman Peter Conte. "TWA was not part of the discussion and not part of the visit."
Seattle Times business reporter Richard Buck contributed to this report.